Conventionally, the linear motion guide units are composed of an elongated guide rail or guide shaft, and a slider which fits over or conforms to the guide rail or guide shaft for sliding movement relative to the guide rail or guide shaft through more than one rolling element of balls or rollers which are allowed to circulate in an endless manner through an endless circuit made up of a load-carrying race defined between the guide rail and the slider, a return passage extending in the slider and turnaround passages lying at opposite ends of the slider. With the prior linear motion guide units with lubricating members, while lubrication between the race and the rolling elements has been ensured with periodic application or resupply of lubricant, advanced linear motion guide units recently become required to meet needs of maintenance-free operation for lubrication over a prolonged interval of time for cost savings of maintenance for lubrication in the machinery and/or installation.
In Japanese Laid-Open Patent Application No. 2007-100 951 which is a commonly-assigned senior application, there is disclosed a linear motion guide unit having lubricant resupply means in which application of lubricant around the rolling elements is done at the turnaround passage to make the lubrication system simpler than ever in construction, along with maintenance-free for steady and positive lubrication. With the prior linear motion guide unit constructed as stated earlier, the end cap has an opening extending from a recess on the outward end surface to the turnaround passage and a lubricant reservoir plate of porous compact impregnated with lubricant fits into the recess on the outward end surface of the end cap. The lubricant reservoir plate has an applicator nose extending through the opening in the end cap to form at the extremity thereof in part the circular wall of the turnaround passage to expose itself to come into engagement with the rollers rolling through the turnaround passage to feed the rolling elements with lubricant through the applicator noses of the lubricant reservoir plate, thereby making application of lubricant around the rollers while rolling through the turnaround passage.
We has developed a linear motion guide unit with a lubricating plate which can be easily attached and/or removed without making an alternation in basic specifications disclosed in Japanese Laid-Open Patent Application No. H 10-205 534 which is also a commonly-assigned senior application. With the linear motion guide unit recited earlier, the lubricating plate is disposed between a spacer and an end seal and attached to a carriage of a slider to travel relative to a guide rail in a way making sliding contact with raceway grooves on the guide rail. The lubricating plate is made of sintered resinous material of porous compact impregnated with oily lubricant. The sintered resinous material is produced after finely powdery synthetic resin has been compacted in a mold under pressure together with the application of heat. The lubricating plate is divided into a denser part and a coarse part which are bound together with a covering.
In another Japanese Laid-Open Patent Application No. 2012-154 438 which is a commonly-assigned senior application, there is disclosed a linear motion guide unit in which lubrication for the rolling elements is carried out in a turnaround passage in an end cap and an applicator nose to come into contact with the rolling elements has a molded density greater than in a lubricant reservoir plate to ensure a longer lubrication-life for proper and steady lubrication, with accompanying sustainable maintenance-free condition for lubrication. The lubricant reservoir plate of porous compact impregnated with lubricant fits in a recess on the end cap to expose the applicator nose integral with the lubricant reservoir plate to the turnaround passage through an opening cut in the turnaround passage to make application of lubricant around the rolling elements by use of the applicator nose. With the lubricant reservoir plate, the applicator nose of the porous compact has the molded density of from 0.60 g/cm3 to 0.70 g/cm3, and the lubricant reservoir plate of the porous compact has the molded density of from 0.40 g/cm3 to 0.60 g/cm3.
With the prior linear motion guide unit constructed as stated earlier, application of lubricant around the rolling elements is carried out in the turnaround passage in the end cap. More especially, the rolling elements while rolling through the turnaround passage in the end cap come into engagement or contact with the applicator nose of the lubricant reservoir plate and in doing so the lubricant is fed around the rolling elements by means of applicator nose of the lubricant reservoir plate. With the linear motion guide unit constructed as stated earlier, more lubricant than a required and sufficient amount for rolling contact of the rolling elements and the races continues to be applied around the rolling elements in the beginning phase of operation. However, after lubricant contained in the lubricant reservoir plate has diminished down to a preselected level, the lubricant continues reducing with a substantially fixed reduction rate per unit distance. This means that lubricant contained in the lubricant reservoir plate, because more consumed at the beginning phase of operation, gets less as compared with an ideal phase where lubricant would continue to decrease from the beginning with the fixed reduction rate per unit. As a result, the maintenance-free interval is reduced.
Advanced linear motion guide units recently have become required to provide maintenance-free operation for lubrication over a prolonged interval of time for reduction in number of maintenance-free steps and reduction in consumed amount of lubricant aiming at saving of resources and environmental impacts. With the linear motion guide units in which the application of lubricant around rolling elements is carried out in the turnaround passage, accordingly, there has been required development of the maintenance-free construction in which the lubricating member is allowed to store lubricant as much as possible as well as lubricant rids itself of more application at the beginning phase of operation to make sure of smooth application of adequate amount of lubricant around the rolling elements application over a prolong period of time.